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Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"

From Toshi Kani <toshi.kani@hpe.com>
Newsgroups linux.kernel
Subject Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"
Date 2016-03-10 20:20 +0100
Message-ID <rbehP-2Wa-11@gated-at.bofh.it> (permalink)
References (6 earlier) <rae0z-1QO-43@gated-at.bofh.it> <rba4y-8hd-5@gated-at.bofh.it> <rbbai-G2-13@gated-at.bofh.it> <rbczp-1Pk-17@gated-at.bofh.it> <rbe8a-2SM-17@gated-at.bofh.it>
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On Thu, 2016-03-10 at 14:04 -0500, Paul Gortmaker wrote:
> [Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
> disabled"] On 10/03/2016 (Thu 18:20) Borislav Petkov wrote:
> 
> > On Thu, Mar 10, 2016 at 09:49:51AM -0700, Toshi Kani wrote:
> > > This confirms the issue - QEMU's virtual Intel CPU does not support
> > > MTRR. 
> > > 
> > > When MTRR is disabled, the kernel does not call pat_init().
> > >  pat_enabled() is still set to true when CONFIG_X86_PAT is set.
> > >  CONFIG_X86_PAT depends on CONFIG_MTRR, and assumes that MTRR is
> > > enabled. 
> > 
> > Aha, so "qemu32" model doesn't support MTRRs but "kvm32" does, for
> > example. And so do the majority of the other CPU types.
> 
> So, I guess that is a qemu bug?  If there is no real silicon out there
> that has no MTRR but does claim PAT, then qemu32 is a flawed CPU type?

It turns out that your qemu's virtual CPU does not support PAT, either. :-) 
 So, it is consistent on this regard.  I will send patches to address this
issue.

Thanks,
-Toshi

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Thread

Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-04 19:40 +0100
  Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-04 22:30 +0100
    Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-07 01:40 +0100
      Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-07 16:20 +0100
        Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-07 23:50 +0100
          Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-08 01:00 +0100
            Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-08 01:10 +0100
              Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-08 01:50 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-08 04:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-08 16:50 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-10 15:50 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-10 17:00 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-10 18:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-10 20:10 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-10 20:20 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-10 20:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-03-11 14:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-11 14:50 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paolo Bonzini <pbonzini@redhat.com> - 2016-03-11 20:20 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-11 23:20 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Bruce Ashfield <bruce.ashfield@windriver.com> - 2016-03-11 23:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Richard Purdie <richard.purdie@linuxfoundation.org> - 2016-03-12 00:50 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-12 13:10 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-10 20:20 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-10 20:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-10 20:40 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Borislav Petkov <bp@suse.de> - 2016-03-10 22:10 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-10 23:30 +0100
              Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-08 04:20 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-08 16:30 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Toshi Kani <toshi.kani@hpe.com> - 2016-03-08 17:10 +0100
                Re: runtime regression with "x86/mm/pat: Emulate PAT when it is  disabled" Paul Gortmaker <paul.gortmaker@windriver.com> - 2016-03-08 17:10 +0100

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